An antenna is a mechanical structure with an associated electrical behavior. Any change to its mechanical structure will affect its electrical performance. Since an antenna radiates energy, it interacts with nearby objects which has the effect of changing the antenna's mechanical nature, and hence, its electrical nature. Therefore, placing an antenna near objects, such as a metal surface, changes the resonant frequency of the antenna.
Patch antennas are ideal for many applications having restricted mounting locations due to their low profile. However, patch antennas are typically narrow-band. When a patch antenna is placed in tight quarters on or near metal surfaces or objects, the surrounding environment can cause a resonant frequency shift that can move the antenna's resonant frequency completely out of band. Currently, antenna designers compensate for this frequency change by customizing a patch antenna to its specific mounting location and environment. Each antenna's design is based on the size of the surface it is mounted to and the unique interference caused by its relative location to other objects. The uniqueness of most locations/environments can make the use of patch antennas costly.